It is knwon that the various slags and cinders from the working and metallurgy of non-ferrous metals such as zinc, lead, copper, chromium, etc. supply materials whose configurations and physical-chemical characteristics vary according to the treatment process applied thereto. Thus, for example, slags from glass furnaces and steel mills can have the form of compact or crystallized alveolar aggregates, vitrified granules, etc.
Most of these slags must, after cooling in the appropriate pit, undergo either fragmentation, as is the case for phosphated or non-phosphated steel mill slags, for example those derived from refining non-phosphorous cast iron, or crushing to a greater or lesser degree as is the case, for example, for steel mill slags from phosphorous cast iron, before utilization in the form of granulate products by adding binders and/or fertilizers.
These crushing and grinding operations of layers of slag and cinder, after cooling in the pit, require high energy consumption because the elements which do not disintegrate immediately are extremely hard; in addition and because of this the machinery employed for this treatment wears rapidly making it necessary to replace frequently the elements designed to fragment and crush slag slabs and aggregates.
True, various means of inducing foaming of slags and thus obtaining multi-cellular masses have been recommended. Among the porophoric, i.e. the foaming agents described, substances such as perlite (French Pat. No. 1,472,795 of Mar. 29, 1966) or carbon black or coal dust rich in volatiles (see for example French Pat. No. 1,489,000 of Sept. 23, 1965) have been recommended. However, perlite, which expands as it crumbles in the slags, causes the latter to increase in volume and in fact coagulate, which is a serious disadvantage for the application envisaged by the invention. In addition, where pulverized coke or coal dust is used, the heat of the molten slag mass is further increased and the injected carbonate material adds no particular property to the slag besides its foaming action and must be considered as wasted.